Commit 11b844b0 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
Browse files

selftests/bpf: Work-around EBUSY errors from hashmap update/delete 



20b6cc34 ("bpf: Avoid hashtab deadlock with map_locked") introduced
a possibility of getting EBUSY error on lock contention, which seems to happen
very deterministically in test_maps when running 1024 threads on low-CPU
machine. In libbpf CI case, it's a 2 CPU VM and it's hitting this 100% of the
time. Work around by retrying on EBUSY (and EAGAIN, while we are at it) after
a small sleep. sched_yield() is too agressive and fails even after 20 retries,
so I went with usleep(1) for backoff.

Also log actual error returned to make it easier to see what's going on.

Fixes: 20b6cc34 ("bpf: Avoid hashtab deadlock with map_locked")
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20201223200652.3417075-1-andrii@kernel.org
parent e7e51805

tools/testing/selftests/bpf/test_maps.c

+42 −6
Original line number Diff line number Diff line
@@ -1312,22 +1312,58 @@ static void test_map_stress(void) 
#define DO_UPDATE 1

#define DO_DELETE 0



#define MAP_RETRIES 20



static int map_update_retriable(int map_fd, const void *key, const void *value,

				int flags, int attempts)

{

	while (bpf_map_update_elem(map_fd, key, value, flags)) {

		if (!attempts || (errno != EAGAIN && errno != EBUSY))

			return -errno;



		usleep(1);

		attempts--;

	}



	return 0;

}



static int map_delete_retriable(int map_fd, const void *key, int attempts)

{

	while (bpf_map_delete_elem(map_fd, key)) {

		if (!attempts || (errno != EAGAIN && errno != EBUSY))

			return -errno;



		usleep(1);

		attempts--;

	}



	return 0;

}



static void test_update_delete(unsigned int fn, void *data)

{

	int do_update = ((int *)data)[1];

	int fd = ((int *)data)[0];

	int i, key, value;

	int i, key, value, err;



	for (i = fn; i < MAP_SIZE; i += TASKS) {

		key = value = i;



		if (do_update) {

			assert(bpf_map_update_elem(fd, &key, &value,

						   BPF_NOEXIST) == 0);

			assert(bpf_map_update_elem(fd, &key, &value,

						   BPF_EXIST) == 0);

			err = map_update_retriable(fd, &key, &value, BPF_NOEXIST, MAP_RETRIES);

			if (err)

				printf("error %d %d\n", err, errno);

			assert(err == 0);

			err = map_update_retriable(fd, &key, &value, BPF_EXIST, MAP_RETRIES);

			if (err)

				printf("error %d %d\n", err, errno);

			assert(err == 0);

		} else {

			assert(bpf_map_delete_elem(fd, &key) == 0);

			err = map_delete_retriable(fd, &key, MAP_RETRIES);

			if (err)

				printf("error %d %d\n", err, errno);

			assert(err == 0);

		}

	}

}